The Puritan Revolution escaped the control of its creators. The parliamentarians who went to war with Charles I in 1642 did not want or expect the fundamental changes that would follow seven years later: the trial and execution of the king, the abolition of the House of Lords, and the creation of the only republic in English history. There were startling and unexpected developments, too, in religion and ideas: the spread of unorthodox doctrines; the attainment of a wide measure of liberty of conscience; new thinking about the moral and intellectual bases of politics and society. God's Instruments centres on the principal instrument of radical change, Oliver Cromwell, and on the unfamiliar landscape of the decade he dominated, from the abolition of the monarchy in 1649 to the return of the Stuart dynasty in 1660.

Its theme is the relationship between the beliefs or convictions of politicians and their decisions and actions. Blair Worden explores the biblical dimension of Puritan politics; the ways that a belief in the workings of divine providence affected political conduct; Cromwell's commitment to liberty of conscience and his search for godly reformation through educational reform; the constitutional premises of his rule and those of his opponents in the struggle for supremacy between parliamentary and military rule; the relationship between conceptions of civil and religious liberty. The conflicts Worden reconstructs are placed in the perspective of long-term developments, of which historians have lost sight, in ideas about parliament and about freedom. The final chapters turn to the guiding convictions of two writers at the heart of politics, John Milton and the royalist Edward Hyde, the future Earl of Clarendon. Material from previously published essays, much of it expanded and extensively revised, comes together with freshly written chapters.